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- Cramwinckel, Margot J., et al.
(författare)
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A Warm, Stratified, and Restricted Labrador Sea Across the Middle Eocene and Its Climatic Optimum
- 2020
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Ingår i: Paleoceanography and Paleoclimatology. - 2572-4517 .- 2572-4525. ; 35:10
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Tidskriftsartikel (refereegranskat)abstract
- Several studies indicate that North Atlantic Deep Water (NADW) formation might have initiated during the globally warm Eocene (56–34 Ma). However, constraints on Eocene surface ocean conditions in source regions presently conducive to deep water formation are sparse. Here we test whether ocean conditions of the middle Eocene Labrador Sea might have allowed for deep water formation by applying (organic) geochemical and palynological techniques, on sediments from Ocean Drilling Program (ODP) Site 647. We reconstruct a long‐term sea surface temperature (SST) drop from ~30°C to ~27°C between 41.5 to 38.5 Ma, based on TEX86. Superimposed on this trend, we record ~2°C warming in SST associated with the Middle Eocene Climatic Optimum (MECO; ~40 Ma), which is the northernmost MECO record as yet, and another, likely regional, warming phase at ~41.1 Ma, associated with low‐latitude planktic foraminifera and dinoflagellate cyst incursions. Dinoflagellate cyst assemblages together with planktonic foraminiferal stable oxygen isotope ratios overall indicate low surface water salinities and strong stratification. Benthic foraminifer stable carbon and oxygen isotope ratios differ from global deep ocean values by 1–2‰ and 2–4‰, respectively, indicating geographic basin isolation. Our multiproxy reconstructions depict a consistent picture of relatively warm and fresh but also highly variable surface ocean conditions in the middle Eocene Labrador Sea. These conditions were unlikely conducive to deep water formation. This implies either NADW did not yet form during the middle Eocene or it formed in a different source region and subsequently bypassed the southern Labrador Sea.
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- Houben, Alexander J. P., et al.
(författare)
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The Eocene-Oligocene transition : Changes in sea level, temperature or both?
- 2012
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 335, s. 75-83
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Tidskriftsartikel (refereegranskat)abstract
- The Eocene-Oligocene Transition (EOT similar to 34 Ma) reflects the onset of major Antarctic glaciation. The primary geochemical signature of the EOT is two similar to 300 kyr spaced shifts in increasing deep-sea oxygen isotope values, possibly reflecting both global cooling a nd/or increasing ice volume. A way to assess the respective contribution of continental ice is to quantify concomitant glacio-eustatic sea level change. This is usually expressed in relatively shallow marine depositional settings. One potentially suitable region is in the Vicentinian Alps, NE Italy, where marginal marine deposits document sea level changes during the;EOT. By correlating stable isotope-, bio- and magnetostratigraphic information between three distant regions, we are able to relate the shallow marine sections to the Pacific oxygen isotope record from Ocean Drilling Program (ODP) Site 1218 of Coxall et al. (2005). Microfacies, sedimentological, and biotic analysis suggests that associated with the first isotope shift (EOT-1) sea level fell similar to 20 m, and with the ultimate shift, the Oligocene Isotope Event 1 (Oi-1) sea level fell some 50-60 m. Distribution patterns of temperature sensitive dinoflagellates from a coeval central Italian section reveal that the early stages of the EOT were accompanied by sea surface cooling, whereas no sustained cooling is noted in association with the Oi-1. This suggests that the initial EOT shift(s) reflect a mixed signal of ice volume and temperature whereas the Oi-1 primarily reflects expansion of the Antarctic cryosphere.
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- Jakobsson, Martin, et al.
(författare)
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The Early Miocene Onset of a Ventilated Circulation Regime in the Arctic Ocean
- 2007
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 447:7147, s. 986-990
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Tidskriftsartikel (refereegranskat)abstract
- Deep-water formation in the northern North Atlantic Ocean and the Arctic Ocean is a key driver of the global thermohaline circulation and hence also of global climate. Deciphering the history of the circulation regime in the Arctic Ocean has long been prevented by the lack of data from cores of Cenozoic sediments from the Arctic’s deep-sea floor. Similarly, the timing of the opening of a connection between the northern North Atlantic and the Arctic Ocean, permitting deep-water exchange, has been poorly constrained. This situation changed when the first drill cores were recovered from the central Arctic Ocean. Here we use these cores to show that the transition from poorly oxygenated to fully oxygenated (‘ventilated’) conditions in the Arctic Ocean occurred during the later part of early Miocene times. We attribute this pronounced change in ventilation regime to the opening of the Fram Strait. A palaeo-geographic and palaeo-bathymetric reconstruction of the Arctic Ocean, together with a physical oceanographic analysis of the evolving strait and sill conditions in the Fram Strait, suggests that the Arctic Ocean went from an oxygenpoor ‘lake stage’, to a transitional ‘estuarine sea’ phase with variable ventilation, and finally to the fully ventilated ‘ocean’ phase 17.5 Myr ago. The timing of this palaeo-oceanographic change coincides with the onset of the middle Miocene climatic optimum, although it remains unclear if there is a causal relationship between these two events.
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- Stein, Ruediger, et al.
(författare)
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Cenozoic Arctic Ocean Climate History : Some Highlights from the Integrated Ocean Drilling Program Arctic Coring Expedition
- 2014. - 1
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Ingår i: Earth and Life Processes Discovered from Subseafloor Environments. - Amsterdam : Elsevier. - 9780444626172 ; , s. 259-293
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Bokkapitel (refereegranskat)abstract
- With the Arctic Coring Expedition (ACEX) (the first Mission Specific Platform expedition within the Integrated Ocean Drilling Program) Expedition 302 in 2004, a new era in Arctic research began. For the first time, a scientific drilling expedition in the permanently ice-covered Arctic Ocean was carried out, penetrating 428 m of Quaternary, Neogene, Paleogene, and Campanian sediment on the crest of Lomonosov Ridge close to the North Pole between 87 and 88°N. By studying the unique ACEX sequence, a large number of scientific discoveries that describe previously unknown Arctic paleoenvironments were obtained during the last decade. Key results include subtropical warm conditions during the Paleocene-Eocene Thermal Maximum and the early-mid Eocene, an episodic freshening of Arctic surface waters in the Eocene, black shales and euxinic conditions in the Eocene Arctic Ocean, and an early onset of Arctic sea ice (Northern Hemisphere glaciation) in the middle Eocene. While these results from ACEX were unprecedented, key questions related to the climate history of the Arctic Ocean on its course from Greenhouse to Icehouse conditions during early Cenozoic times remain unanswered, in part because of poor core recovery, and in part because of the possible presence of a major mid-Cenozoic hiatus within the ACEX record. Furthermore, the ACEX sites remain the one and only drill holes in the entire central Arctic Ocean to date. In order to decipher the paleoclimatic and tectonic history of this unique and sensitive but still not well-known region on Earth, future scientific Arctic drilling is certainly needed.
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- van Mourik, Caroline A., 1969-
(författare)
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The Greenhouse - Icehouse Transition : a dinoflagellate perspective
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Through the analysis of the stratigraphic and spatial distribution of organic walled dinoflagellate cysts (dinocysts) from climatologically and oceanographically key sites, this project aims to contribute to a better understanding of the Eocene-Oligocene (E/O) environmental changes and their timing. A central issue is to identify the global environmental changes which are responsible for the Eocene cooling and its underlying mechanisms with the focus on the Oligocene isotope-1 (Oi-1) event, thought to mark the onset of major Antarctic glaciation.Two low-latitude sites were selected, Blake Nose (western North Atlantic) and Massignano (central Italy). For the first time a coherent taxonomy and biostratigraphy of dinocysts was established for the late Eocene at these latitudes. A high resolution correlation was established between the Massignano E/O Stratotype Section and the stratigraphically more extended ‘Massicore’. The composite section was used to analyse sea surface temperature (SST) change across the greenhouse-icehouse transition by means of dinocyst distribution.At Massignano, the Oi-1 event was recognised both qualitatively and quantitatively. In the power spectrum of the SSTdino the ~100 and ~400 kyr eccentricity cycles may be distinguished and correlated with La04. When orbitally tuned, the E/O GSSP dates ~100 kyr older than the Oi-1 event. The boundary’s age could either be ~33.75 or ~34.1 Ma, both differ significantly from the ~33.9 Ma age in the GTS 2004.Furthermore, when the data from the low-latitude sites were combined with extensive datasets from the Proto North Atlantic and adjacent regions, a suite of species sensitive to changes in SST was recognised. Their first and last occurrences reflect seven distinct phases of decreasing SSTs during the Middle Eocene to earliest Oligocene.These results clearly indicate that atmospheric cooling together with higher frequency orbital forcing played a key role in the transition from the Greenhouse to the Icehouse world.
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